Firing rate reducer for automatic firearms



J1me 1956 c. E. SIMPSON 2,74

FIRING RATE REDUCEZR FOR AUTOMATIC FIREARMS Filed Dec. 10, 1952INVENTOR. Elurence E- 51m sun ATTORNEYS FIRING RATE REDUER FOR AUTOMATICFIREARMS Clarence E. Simpson, Wilbraham, Mass., assignor to the UnitedStates of America as represented by the Secretary of the ArmyApplication December 10, 1952, Serial No. 325,239

6 Claims. (Cl. 89-130) (Granted under Title 35, U. S. Code (1.952), sec.265) The invention described herein may be manufactured and used by orfor the Government for governmental purposes without the payment of anyroyalty thereon.

This invention relates to a fire control mechanism for automaticfirearms and particularly to a mechanism for delaying the rate of fireof the firearm.

Modern warfare demands a large volume of fire from automatic firearms ata rapid rate. However in the attempt to design firearms of lesserweight, the cyclic rate of the firearm increased as the weight of thereciprocating parts decreased. Thus while a larger volume of fire at ahigh rate was capable of'being produced by such firearms, the rate offiring was excessively fast so that such a high rate of fire wore outthe barrels unduly fast. Another drawback to such high rate of fire wasthe inability of the shooter to accurately concentrate his fire on atarget.

In order to slow down the rate of fire of such firearms various ratereducing devices have been resorted to. Unfortunately the shape, size,and operation of many prior art rate reducing devices preclude their usein modern design of firearms. This is particularly true when such amechanism must be located in the pistol grip of the firearm and combinedwith the fire control mechanism thereof.

Accordingly, it is an object of this invention to provide a fire controlmechanism for an automatic firearm having a delaying mechanism whereby areduced rate of automatic fire can be obtained.

Another object of this invention is to provide a fire control mechanismhaving full automatic fire and semiautomatic fire control.

A further object of this invention is to provide a delaying device for afire control mechanism which is simple and positive in action.

Still another object of this invention is to provide a fire control andrate reducing mechanism for an automatic firearm capable of beingcontained in the pistol grip of a firearm.

The specific nature of the invention as well as other objects andadvantages thereof will clearly appear from a description of a preferredembodiment as shown in the accompanying drawings in which:

Fig. 1 is a fragmentary longitudinal sectional view of the trigger guardof a firearm embodying this invention;

Fig. 2 is an exterior left side view of the trigger guard; and

Fig. 3 is a cross-sectional view taken along the line 33 of Fig. 1.

The fire control mechanism of this invention is contained in a triggerhousing 10. Such housing is arranged to be secured to a firearm (notshown) and comprises a trigger guard 11 and apistol grip 12. Triggerhousing is recessed at 13 so that the elements .of this invention can bemounted in such recess. A trigger 14 is mounted in the forward end ofrecess 13 and is pivotally secured to housing 10 by a transverse pin 15.Trigger 14 has a finger portion 16 of conventional construction.

nited t e Patent The upper end of trigger 14 is bifurcated as shown at17 and a button 18 is mounted within such bifurcation for transverseslidable movement. Button or block 18 is cylindrical and is providedwith a reduced diameter end portion 24 for a purpose as will laterappear. Such button is mounted on a pin 19 provided with a head 20. Thehead 24) of pin 19 has a conical shaped end 21 which is engageable by'ascrew 22 transversely secured in the trigger housing 10. Such screw isprovided with an end 23 having a sloped surface corresponding to thesloped end 21 of pin 19. Screw 22 cooperates with pin 19 to movebutton18 as will be later described.

A washer-like spring 25 is provided within bifurcation 17 surroundingpin 19 to normally bias button 18 to the right asshown in Fig. 3. Head20 of pin 19 is constructed to contact the reduced diameter end ofbutton 13 at all times so that button 18 may be forced to the leftagainst the bias of spring 25 when the conical head 20 of pin 19contacts the correspondingly shaped end of screw 22, as will be laterdescribed. A third pin 26 is transversely mounted at the top of trigger14 as shown in Figs. 1 and 3.

A sear 27 is pivotally mounted within recess 13 of trigger housing 19 bya transverse pin 28. Such sear is mounted substantially above trigger 14and sear 27 is provided with a forwardly projecting end 29 having asloped surface 30 thereon. The forward end 29 of sear 27 rests on button18 while the sloped end 30 thereof is engageable with pin 26 as will belater described. The other end 31 of sear 27 is provided with a squaredend 32 which is engageable with a scar notch 33 provided on theunderside of a bolt 34 shown in outline horizontally disposed above thetrigger housing 10 in Fig. l.

A toggle 35 is pivotally secured to end 31 of sear 27 by a transversepin 36. Such toggle is provided with an upwardly projecting heel 37which is engageable with the underside of bolt 34. A rearwardly anddownwardly projecting toe 38 is provided on toggle 35 which contacts asear actuator 39 for a purpose to be later described. On the undersideof sear 27 there is provided a downwardly projecting cylindrical boss 40which serves as a seat for one end of a spring 41. A corresponding andoppositely disposed boss 42 is provided on the upper side of trigger 14on which the other end of spring 41 is mounted.

Actuator 39 comprises a substantially cylindrical bar provided with anintegral axially disposed spring guide 43 on the bottom end thereof.Actuator 39 is slidably contained within a tubular housing 44 which inturn is contained within pistol grip 12. Such housing is substantiallyvertically disposed therein and also contains a spring 45, one end ofwhich abuts the bottom of actuator 39 cooperating with spring guide 43to retain such spring thereon. An annular groove 46 is provided'onactuator 39 and a latch 47 projects through an opening 48 in tubularhousing 44 for engagement with groove 46. Latch 47 is maintained out ofengagement with groove 46 by a knob or handle 49 attached to latch 47.Any suitable detent means may be provided to yieldingly secure handle 49in either of two positions whereby latch 47 is maintained out ofengagement with groove 46 or maintained in engagement therewith. Latch47 is utilized to hold or to secure actuator 39 in a depressed positionfor semi-automatic fire as will be later described.

I A selector 50 is transversely mounted within recess 13 of triggerhousing 10 directly underneath sear mounting pin 28. Selector 50 isprovided with two flat surfaces 51 is provided to rotate selector 50 tothe desired position and is held therein by any suitable detent means.By the use of selector 50 either full automatic fire or reduced rateautomatic fire may be readily obtained as will now be described.

Operation The fire control mechanism of this invention is preferablyutilized with a firearm adapted to shoot from the open bolt position. InFig. 1 bolt 34 is shown in the retracted position and held thereby searend 32 being in engagement with the shoulder produced by notch 33 inbolt 34. With the selector set in the position shown in Fig. 1 so thatthe flat surface 51 faces lug 53, the fire control mechanism is set forfull automatic fire.

In the position of the parts shown in Fig. l sear nose 29 rests on topof the larger diameter portion of button 18. Thus when trigger 14 ispulled rearwardly such trigger pivots about pin 1.5 in a clockwisedirection carrying therewith button 18. Nose 29 of scar 27 is thusforced upwardly and in a counter-clockwise direction thereby forcing end32 of scar 27 out of engagement with notch 33 whereupon bolt 34 movesforwardly to the battery position. Sear 27 is held out of engagementwith bolt 34 as long as trigger 14 is depressed. With sear 27 thus helddown, toggle 35 is likewise held downwardly and in contact with actuator39. In this setting of the fire control mechanism the actuator has noeffect on toggle 35 as such toggle is maintained in contact with theactuator by sear 27. The rate of fire of the firearm with the firecontrol mechanism set for full automatic fire as just described will bethe normal cyclic rate obtainable without any delay or impedance in thefiring of the cartridge. Full automatic fire may be stopped by releasingtrigger 14.

When such trigger is released, sloped end of sear 27 is raised intocontact with pin 26 on trigger 14 of the recoil stroke of bolt 34. Onsuch stroke of the bolt a lug 54 thereon contacts a cam 55 of sear 27thereby sharply depressing sear end 32 and toggle 35. Toe 38 of togglethen strikes actuator 39 smartly driving such actuator downwardly.Meanwhile spring 41 biases sear end 32 into notch 33 as bolt 34 startsforwardly whereby such bolt is retained in the open position. Shortlyafter such action has taken place actuator 39 has been biased upwardlyby spring to strike toe 38 of toggle 35 thereby tending to pivot suchtoggle about heel 37 and to disengage sear 27 from bolt 34.

However as pin 26 is engaging sloped end 30 of scar 27 such is notpossible. The reason therefore is due to the bias of trigger spring 41being greater than the force with which actuator 39 strikes toggle 35coupled with the fact that the leverage advantage of trigger 14 aboutits pivot point is substantially greater than that of toggle 35. Thusthe rate reducing device is retained relatively inoperative when thetrigger is released in order to cease firing.

When selector 5!) is rotated so that flat surface 52 is disposedopposite lug 53 on trigger 14, the control mechanism is then set forreduced rate of automatic fire. In such position of the selector,trigger 14 may now be pulled rearwardly a greater distance than for fullautomatic fire. Hence as trigger 14 is pulled rearwardly nearly to thelimit of its movement as governed by lug 53, the head portion 20 of pin19 engages screw 22. The sloped end of such screw and head portion 20 ofsuch pin cooperate to force pin 19 to the left from the position asshown in Fig. 3 against the bias of spring 25 whereupon the largerdiameter of button 18 is moved away from sear 27, thus sear 27 isrelatively free to pivot about pin 28 without restraint from button 18.

Initially when the trigger is pulled rearwardly the nose 29 of scar 27resting on the large diameter portion of button 18 forces such endupwardly in the same manner as described for automatic fire. Thus end 32of sear 27 is rotated out of engagement with notch 33 of bolt 34allowing such bolt to go into battery position. The trigger meanwhilehas been pulled to the extreme rear position whereupon button 18 hasbeen cammed to one side so that sear nose 29 no longer rests thereon asabove described. On the recoil stroke of bolt 34, lug 54 provided on theunderside thereof and rearwardly of notch 33, strikes end 32 of scar 27thereby depressing such sear and simultaneously driving toggle 35downwardly against actuator 39 whereupon the impact from such blowforces actuator 39 downwardly within tubular housing 44.

As soon as notch 33 of bolt 34 comes opposite end 32 of sear 27 on thecounter-recoil stroke of bolt 34, spring 41 biases sear end 32 upwardlyinto engagement with sear notch 33 thereby holding bolt 34 in the openposition. Meanwhile, however, actuator 39 is still moving downwardly intubular housing 44 and at the end of such movement spring 45 returnssuch actuator upwardly. The bias of such spring however is sufficientlygreat to impart considerable momentum to actuator 39 and such actuatortherefore strikes toe 38 of toggle 35 a smart blow whereupon end 32 ofscar 27 is forced out of engagement with notch 33. This arrangement ispossible because heel 37 of toggle 35 acts as a fulcrum and when a forceis exerted on toe 38 of toggle 35 the other end of such toggle beingpivotally secured to sear end 32 by pin 36, forces end 32 of sear 27 outof engagement with notch 33 whereupon bolt 34 is permitted to goforwardly again to the battery position. This cycle will be repeated aslong as the trigger is held rearwardly or until the ammunition isconsumed. Release of trigger 14 at any time stops the firing in the samemanner as described for full automatic fire.

It should therefore be readily apparent that the delay introduced by thelength of time it takes the actuator to travel from the position shownin Fig. l to the bottom of housing 44 and up again is appreciable, thusthere is introduced a delay period before the sear 27 is released, whichmaterially slows down the firing rate of the firearm.

The device is readily set for semi-automatic fire when the selector ispositioned to produce a reduced rate of automatic fire. Latch 47 isrotated into engagement with actuator 39 when such actuator is manuallydepressed by knob 59 so that such latch can engage groove 46 to holdactuator 39 in such depressed position. Slots 58 in housing 10 permitknob 59, attached to actuator 39, to depress such actuator downwardly.Thus toggle 35 cannot act on actuator 39 and hence such actuator will beineffective to trip sear end 32 out of engagement with notch 33. Thussemi-automatic fire is also obtained with this fire control mechanism.

From the foregoing description it is clearly apparent to those skilledin the art that there is here provided a compact arrangement of elementsfor a fire control mechanism that are readily contained in the pistolgrip of the trigger housing. Not only does the fire control mechanism ofthis invention provide for full automatic fire and semi-automatic firebut also a reduced rate of fire. The means utilized for delaying thefiring rate of the firearm with which this fire control mechanism isemployed is not only unique in arrangement but simple and positive inoperation. The various elements of this invention are of simple andrugged construction thereby producing a dependable and positive firecontrol mechainsm.

I claim:

1. In a firearm, a reciprocating bolt mounted therein for movementbetween a battery and recoil position, said bolt having a scar engagingnotch with a camming surface rearwardly thereof and a flat surfacetherebetween, a trigger guard mounted to said firearm, a triggerpivotally mounted in said trigger guard and operable to a first andsecond pulled position, a sear pivotally mounted in said trigger guardand movable into and out of engagement with said bolt, a selectorrotatably mounted in said trigger guard and having a first and secondflat surface disposed at an obtuse angle to each other, an upstandinglug on said trigger arranged for cooperation with said selector wherebythe degree of movement of said trigger to said first pulled position islimited by said first surface of said selector and the degree ofmovement of said trigger to said second pulled position is limitedbysaid second surface of said selector, blocking means slidably mounted onsaid trigger and movable therewith for pivoting said sear to adisengaged position when said trigger is pulled to said first position,cam means adjustably mounted in said trigger guard for moving saidblocking means to an inoperative position when said trigger is pulled tosaid second position whereby said sear is permitted to reengage saidnotch at the recoil position during reciprocation of said bolt, a togglepivotally secured to the rear end of said sear, said toggle having adownwardly depending toe portion and an upwardlyextending heel portionfor cooperation with said flat surface of said bolt, an actuatorslidably mounted in said trigger guard provided with spring means forurging said actuator upwardly against said toe of said toggle, springmeans on said trigger for biasing said sear to an engaged position, saidspring means operative in said second position of said trigger formoving said sear to an engaged position and whereby reciprocatingmovement of said camming surface on said bolt in the recoil positioncams said toe of said toggle downwardly thereby deflecting said actuatordownwardly and whereby recovery of said actuator forces said toggleupwardly in a clockwise direction thereby disengaging said sear fromsaid notch of said bolt when said heel portion of said toggle contactssaid flat surface of said bolt.

2. In an automatic firearm having a receiver, a trigger housingdepending therefrom, and a longitudinally reciprocal bolt slidablebetween a battery and a retracted position, the combination of a pivotalsear for holding the bolt in the retracted position, a trigger pivotallymounted at a point forwardly of and below the pivot point of said sear,a cylindrical member transversely mounted for slidable movement on saidtrigger and in contact with the underside of said sear whereby actuationof said trigger lifts said cylindrical member to pivot said sear out ofengagement with the bolt, a spring intermediate said trigger and saidsear rearwardly of the respective pivot points thereof for urging saidsear into engagement with the bolt and simultaneously urging saidtrigger to the released position, said cylindrical member having an endportion of reduced diameter, cam-means in the trigger housing forimparting a transverse movement to said cylindrical member after releaseof said sear from the bolt but during the continued actuation of saidtrigger whereby said reduced diameter portion of said cylindrical memberis vertically aligned with the front end of said sear to permit a returnthereof into engagement with the bolt under the bias of said searspring, a toggle pivotally secured to the rear end of said sear, aspring-biased actuator slidably mounted in the trigger housing forsubstantially vertical movement from and toward contact with theunderside of said toggle, and an inclined cam surface on the undersideof the bolt for actuating said toggle to depress said actuator wherebythe upward recovery movement thereof pivots said toggle tosimultaneously pivot said sear out of engagement with the bolt wherebythe interval of engagement between said scar and the bolt serves toretard each cycle of automatic fire.

3. In an automatic firearm having a receiver, a trigger housingdepending therefrom, a trigger guard and pistol grip included in thetrigger housing, and a longitudinally reciprocable bolt slidable betweena battery and a retracted position, a pivotal sear for holding the boltin the retracted position, a trigger pivotally mounted at a pointforwardly of and below the pivot point of said sear, a springintermediate said sear and said trigger rearwardly of the respectivepivot points thereof for urging said sear to pivot in a clockwisedirection into engagement with the bolt and simultaneously urging saidtrigger in a counterclockwise direction toward the released positionthereof, said trigger having anupper bifurcated portion, a transversepin slidably mounted in said bifurcated portion, said pin having anenlarged head portion projecting from the side of said bifurcatedtrigger portion, a cylindrical member slidably mounted on saidtransverse pin and having a reduced diameter portion on one end thereof,spring means normally biasing said cylindrical member against saidenlarged head portion of said transverse pin and against the side ofsaid bifurcated portion of said trigger whereby clockwise pivotalmovement of said trigger lifts said cylindrical member to pivot saidsear in a counterclockwise direction out of engagement with the bolt, acam stud fixedly mounted in the trigger housing to contact said enlargedhead portion of said transverse pin during clockwise pivoting of saidtrigger and thereby impart transverse movement to said cylindricalmember after release of said sear from the bolt whereby said reduceddiameter end of said cylindrical member is vertically aligned with thefront end of said sear to permit reengagement thereof with the boltunder the bias of said sear spring, a toggle pivotally secured to therear end of said sear, said toggle having an upwardly projecting heelportion and a downwardly projecting toe portion, a spring-biasedactuator slidably mounted in the pistol grip portion of the triggerhousing for reciprocal vertical movement from and toward contact withsaid toe portion on said toggle, an inclined cam surface on theundersideof the bolt for contacting said heel portion on said toggle duringrecoil movement and thereby pivoting said toggle to depress saidactuator, said toggle being arranged to pivot said sear in acounterclockwise direction out of engagement with the bolt in responseto the clockwise pivotal movement imparted to said toggle by the upwardrecovery movement of said actuator whereby the interval of engagementbetween said sear and the bolt serves to retard each cycle of boltoperation during movement thereof into battery position, and selectormeans for limiting the clockwise pivotal movement of said trigger toprevent contact of said fixed stud in the trigger housing with saidenlarged head portion on said transverse pin whereby said sear iscontinuously held out of engagement with the bolt to eifect unretardedautomatic fire while said trigger is held in the pivoted position.

4. In an automatic firearm having a receiver, a trigger housingdepending therefrom to terminate in a pistol grip portion, a bolt havinga sear notch in the underside thereof and slidably mounted in thereceiver for longitudinal recoil and counterrecoil movement, a pivotalsear having spring means normally urging the rear end thereof intoengagement with the sear notch to hold the bolt in a retracted position,and a pivotal trigger having means for imparting counterclockwisemovement to the sear to release the bolt from the retracted positionthereof, a rate reducing mechanism comprising means operative during thecompletion of the firing movement of the trigger for disconnecting thesear therefrom to permit reengagement thereof with the sear notch of thebolt during the counterrecoil movement thereof, an actuator slidablymounted in the pistol grip for movement toward and away from theunderside of the bolt, a toggle member pivotally secured to the rear endof the scar and having an upwardly projecting heel portion and adownwardly extending toe portion, a spring normally urging said actuatorupwardly to contact said toe portion on said toggle member and forcesaid heel portion thereof against the underside of the bolt, and cammeans on the underside of the bolt rearwardly of the sear notch thereinfor pivoting the sear in a counterclockwise direction during recoilmovement of the bolt and thereby imparting a corresponding movement tosaid toe portion of said toggle member for depressing said actuatoragainst the bias of said spring whereby the recovery movement thereofpivots said toggle member in a clockwise direction about said heelportion as a fulcrum to simultaneously withdraw the sear out ofengagement with the sear notch of the bolt to permit completion of thecounterreeoil movement thereof.

5. The combination defined in claim 4 wherein the rear end of the boltis of reduced diameter and wherein said cam means comprises an upwardlyand rearwardly inclined surface on the underside of the bolt between thelarger and smaller diameter portions.

6. in a firearm having a reciprocal bolt, a spring-biased pivotal searfor holding the bolt in a retracted position, and a pivotal trigger foractuating the sear to release the bolt, the combination of means fordisconnecting the sear from the trigger during the firing movementthereof subsequent to the release of the bolt to free the sear fromrcengaging the bolt during the counterrecoil movement thereof, arotatable selector having a first stop surface for halting the firingmovement of the trigger prior to the disconnecting of the sear therefromwhereby the sear is held out of engagement with the bolt to provideautomatic fire until the trigger is returned to the prefired positionthereof, said selector having a second stop surface for halting thefiring movement of the trigger subsequent to the disconnecting of thesear therefrom whereby the sear reengages the bolt during counterrecoilthereof, a toggle member pivotally secured to the rear end of the sear,an upwardly biased actuator engageable with the free end of said togglemember, cam means on the underside of the bolt for pivoting the sear ina counterclockwise direction during recoil movement of the bolt toimpart a corresponding movement to said toggle member and depress saidactuator whereby the recovery movement thereof pivots said toggle memberagainst the underside of the bolt to simultaneously withdraw the searout of engagement with the bolt and thereby provide a reduced rate ofautomatic fire when the firing movement of the trigger is halted by saidsecond stop surface on said selector, means for manually depressing saidactuator, and latch means for retaining said actuator in the manuallydepressed position thereof out of contact with said toggle memberwhereby the sear engages the bolt until the trigger is returned to theprefired position thereof and again retracted thereby providingsemiautomatic operation.

References Citcd'in the file of this patent UNITED STATES PATENTS1,318,214 Logan Oct. 7, 1919 1,518,355 Reibel Dec. 9, 1924 2,384,832Gilligan Sept. 18, 1945 2,384,854 Simpson Sept. 18, 1945 FOREIGN PATENTS579,096 Germany June 21, 1933 999,340 France Oct. 3, 1951

